Rewrite Scala sample code by using a Scala native http client library

[osklyarenko]

This code is using OKHttp https://github.com/verygoodsecurity/vgs-proxy-examples/blob/master/scala/scala-example/src/main/scala/example/Example.scala

OKHttp is a java http client library, so it is a better fit for java samples. According to https://www.implicitdef.com/2015/11/19/comparing-scala-http-client-libraries.html Dispatch could be a popular choice in the Scala world. So we should be using it (or similar library) instead